Choosing a computer: examining the CPU

JPCT 150713 Alan Stainer. Photo by Derek Martin

Published:08:47Sunday 28 June 2015

With the Windows 10 release date drawing nearer, some of you may be thinking about buying a new PC. It can be confusing at the best of times with all the acronyms and funny numbers, so exactly how do you choose?

Let’s break it down into byte (deliberate misspelling) sized chunks, by looking first at the CPU.

So what exactly is a CPU anyway? It stands for Central Processing Unit, which sounds a bit like a factory in a science fiction film where they churn out genetically or psychologically modified humans. In reality it is a computer chip that could be said to be the brains of the operation. Instructions and data go in and the CPU processes it all and tells the other parts of the computer what to do.

Simple right? What about all those funny numbers?

Well, let’s start with the slot. It is important if you are replacing a CPU or building your own PC to know which slot you have. You see different motherboards (that’s the circuit board everything plugs into) use different slots, as do CPUs. If you choose a CPU that doesn’t fit, you aren’t going to go anywhere very fast and will need to buy a different CPU. The two main brands of CPU (Intel and AMD) each use multiple slot types and you will find that motherboards are either Intel or AMD compatible. So the best advice here is to check the documentation for your mother board.

Okay, that’s the geeky build your own PC bit done. The next most obvious number to look out for is the speed. If you find a CPU with the speed measured in MHz, then you must be travelling with Dr Who, because that is ancient history. CPUs these days are all in the GHz range, with higher numbers being better. To give you a rough idea, if a 4G Hz processor was a motorbike, you would be clinging on for dear life. If it was a 1.2 GHz processor, then you’d be happily cycling around town on your moped.

Processor speed isn’t the only thing to look out for. You also need to be looking for the number of processor cores. Each core if effectively a processor unto itself. While you don’t necessarily get twice the speed with a dual core processor compared with a single core, it does mean the processor can do more than one thing at a time. Some processors can have up to eight physical cores.

The number of cores isn’t the end of it. Intel chips are capable of hyperthreading. That’s basically some technical wizardry that means each physical core acts like two. So an eight core chip behaves like a sixteen core chip! Intel processors are generally regarded as faster than AMD processors. The hope is that AMD will catch up at some point so there is more competition at the higher end of the market again.

Anyway, another number to watch for is the cache size and type. Processor cache is basically a small amount of very fast memory. This means the processor spends less time accessing the dedicated RAM, which makes things just that little bit quicker. You will see it written down like 20MB L3 cache. L3 is current standard, with L2 being older, etc. The higher the number of MBs listed, the better.

Finally, some processors (like the Intel i series chips) also perform the same duties as a graphics card. That’s a subject for another time.